Hydrogen generators have been known, in which a reformed gas composed mainly of hydrogen is generated in such a manner that a material containing an organic compound composed of at least carbon and hydrogen is passed, in the form of a steam-containing material gas, through a catalyzing portion filled up with a particulate reforming catalyst whereby the material gas is subjected to steam reforming. This type of hydrogen generator is suitable for use in fuel cell systems. In the fuel cell systems, the reformed gas is typically subjected to reduction in concentration of carbon monoxide in a shift converter and in a carbon monoxide selective oxidization device, and is then supplied to a fuel cell.
A conventional hydrogen generator has a reformer body which includes the above described catalyzing portion. The reformer body is supplied with a material, water, and a fuel for combustion, combusts the fuel for combustion therein, and discharges a combustion gas and a reformed gas. To be specific, within the reformer body, vaporization of water or water and material and steam reforming reaction proceed, by utilizing combustion heat. During startup operation and shutdown operation of the hydrogen generator, the combustion heat causes thermal deformation within the reformer body. The catalyst in the catalyzing portion is partially crushed by application of pressure resulting from the thermal deformation, thereby causing a flow passage of a reforming reaction gas in the catalyzing portion to be somewhat clogged. This arises a problem that capability of the hydrogen generator degrades. In view of this problem, patent document 1 discloses a structure of a fuel reformer aimed at reducing crush of the particulate reforming catalyst due to the thermal deformation of a reforming pipe. As used herein, the term “reforming reaction gas” refers to steam-containing material gases which are generated by vaporization of water and a material and reformed gases, and that flow through the catalyzing portion.
FIG. 11 is a longitudinal sectional view of the fuel reformer disclosed in embodiment 3 of the patent document 1.
As shown in the FIG. 11, at a burner 105 in a reformer body 100, a fuel introduced from a fuel inlet 153 is combusted by combustion air taken in from an air inlet 154 and thereby a high-temperature heat medium 151 which is a combustion gas is generated. The heat medium 151 flows downward along an inner peripheral surface of an inner tubular body 182 of a reforming pipe 108. Following this, while flowing within a heat medium passage 152, the heat medium 151 flows upward along an outer peripheral surface of an outer tubular body 183, and thereafter is discharged to outside the reformer body 100 from a heat medium outlet 171. During this, the heat medium 151 heats a catalyst layer 103 mainly from the inner peripheral surface side of the inner tubular body 182 of the reforming pipe 108, and also heats a material gas 109 flowing within an outer tubular space 187 from the outer peripheral surface side of the outer tubular body 183.
At this time, a particulate reforming catalyst P present in the catalyst layer 103 is supplied and heated with heat that is transferred from the heat medium 151 via the inner tubular body 182. Thereby, in the reformer body 100, the catalyst layer 103 is sufficiently heated. Meanwhile, the water-containing material 109 flows into the reformer body 100 from an inlet 871, first flows downward within the outer tubular space 187, then flows back in the opposite direction at a lower end of an intermediate tubular body 181, enters the catalyst layer 103, and flows upward within the catalyst layer 103. During this, the material 109 is heated mainly in the outer tubular space 187 by the heat medium 151. The water and the material 109 heated by the heat medium 151 is vaporized into a material gas containing steam and is reformed into a hydrogen-rich reformed gas 110 by catalytic reforming action exhibited by the particulate reforming catalyst P which has been heated by the heat medium 151 to a required temperature. The reformed gas 110 thus obtained is supplied to outside the reformer body 100 from an outlet 861. Note that the water or the material 109 flowing into the reformer body 100 from the inlet 871 may be either in the form of steam or gas.
The catalyst layer 103 of the reformer body 100 is disposed in an inner tubular space 186 formed within the reforming pipe 108, and includes a plurality of respective catalyst layers 131 and a plurality of separating plates 132. Each separating plate 132 is a annular metal plate, has an outer diameter dimension that defines, between itself and the intermediate tubular body 181, a gap having a dimension smaller than a outside dimension of the particulate reforming catalyst P, and is firmly fixed, at its inner peripheral surface, to an outer peripheral surface of the inner tubular body 182 by welding or other means. A number of through holes having a smaller diameter than the outside dimension of the particulate reforming catalyst P are formed on the separating plate 132. The plurality of separating plates 132 of the catalyst layer 103 are arranged in such a manner that adjacent separating plates 132 are spaced apart from each other at equal intervals along a direction of a center axis X of the inner tubular space 186.
Each catalyst layer 131, whose lower surface is defined by its associated separating plate 132, is formed by filling with the particulate reforming catalyst P inside the inner tubular space 186 having the periphery defined by the intermediate and inner tubular bodies 181 and 182. Each catalyst layer 131 is formed such that a space 311 is defined between its upper surface and an adjacently overlying separating plate 132. Note that filling the catalyst layers 131 except for an uppermost catalyst layer 131 with the particulate reforming catalyst P is carried out from a through hole 811 formed in the intermediate tubular body 181 so as to have a greater diameter than the outside dimension of the particulate reforming catalyst P, in a state where at least an upper plate 185 or an outer tubular body 183 is not mounted to the reforming pipe 8. After completion of filling with the particulate reforming catalyst P, the through hole 811 is air-tightly closed by a closing plate 812. Filling the uppermost catalyst layer 131 with the particulate reforming catalyst P is carried out after connection of the intermediate tubular body 181, the inner tubular body 182, and the outer tubular body 183 by a closing plate 184 or the like.
Thereby, the space 311 is formed above an upper surface of an upper layer portion of each catalyst layer 131 and is not filled with the particulate reforming catalyst P. For this reason, the particulate reforming catalyst P present in the vicinity of the upper surface of the each catalyst layer 131 is allowed to move upward almost freely and is subjected to only a slight force caused by friction or the like. Thus, it is proposed that the level of force applied to the particulate reforming catalyst P can be reduced in contrast to the catalyst layer of a conventional fuel reformer.    Patent document 1: Japanese Laid-Open Patent Application Publication No. Hei. 8-208202